Rhenium plating



NOV. 4, 1952 E 2,616,840

RHENIUM PLATING V Filed NOV. 12, 1948 2 SHEETS-SHEET 1 FIG. I

il x H6. 2 INENTOR ROBERTO LEV Nov. 4, 1952 R. LEVI 2,616,840

RHENIUM PLATING Filed Nov. 12, 194 8 2 SHEETS--SHEET 2 ir ma -5 FIG-15c.

INVENTOR R 0 BE RT 0 L EV! Patented Nov. 4, 1952 RHENIUM PLATING Roberto Levi, New York, N. Y., assignor to Philips Laboratories, Inc., Irvington-on-Hudson, N. Y.

Application November 12, 1948, Serial No. 59,674

My invention relatesto. a method for plating rhenium upon a base metal giving a durable, impervious rhenium. layer. e v

Rhenium is an element occurringin minutely small amounts throughout the surface of the a desirable plating material.

nickel, chromium and the like.

above room temperature.

paratus for electrodepositing of rhenium. earth. It is a hard bright metal when in a mas- Fig. 2 showsone form of apparatus for preparsive state, resembling tungsten or rhodium. ing rhenium plating in accordance with the in- Further characteristics of rhenium are its exvention. I tremely high melting point a high resistance to Fig. 3a shows an X-ray diffraction photograph attack by hydrochloric acid, a volatilization less indicating the crystallographic structure of than tungsten in vacuo,-and an electron emisrhenium and the characteristic lines'thereof, sivity approximately equivalent to tungsten; it is Fig. 3b shows an X-ray diffraction photograph V of the crystallographic structure of the element My invention is particularly advantageous to tungsten.

connection with plating rhenium upon other less Fig. 3c shows an X-ray difiraction photograph expensive metals, giving. such other metals 9. immediately after plating of rhenium upon a hard, massive coating of rhenium. As I have base of tungsten. obtained especially advantageous results using Fig. 3d shows an X-ray diffraction photograph refractory metals, for example tungsten and of plated rhenium on the base of a tungsten metal molydenum, as base metals, 1 shall describe the after treatment in accordancewith the method invention in this connection. However, the inof the invention. vention is not limited to the use of tungsten and Referring to Fig. 1, a base metal cathode, for molydenum or refractory basemetals, but exexample of tungsten tobe plated, is cleaned and tends to'other metals Such as platinum, rhodium, immersed in an electroplating solution 5. This 2 electroplating solution 5 may contain for exhe electrodeposition 0 rhenium, P is ample: potassium perrhenataKReOa 11 grams known. W t e p oper co of c factors per liter; concentrated sulphuric acid, H2804, as current de s y, hydrogen 1 Concentration, the solution having a pH=0.9. The temperature temperature, etc., it has been possible to obtain f th l ti maybe b t t 45 0, other a r massive electrodeposition 0f rhenium from sulphate baths are known utilizing various aque- Var aqueous plating 801111110115 Containing ous solutions of rhenium compounds and indeed Compounds bf rhenium- Such kn -processes other baths such as phosphate and alkaline baths have in common at least two serious objections. maybe employed in accordance t known The first is th rapi Oxidation of. the deposited cedures, with the proper adjustment of hydrogen rhenium after a few days of e po to moist ion concentration, temperature, etc. Element I air at ro temperature- Such Oxidation shows an anode which maybe made of platinum. verts the entire deposited layer to perrhenic acid. The cathode and anode, 2 d respectively, are T t ng objection is be found in the fact connected as electrodes in an electric circuit, in that even a t b platmg 9 'P made by accordance with the ordinary techniques of platj ordinaltfly thlck .electro' 40 ing, including a source of direct current potenqeposit-pn of rhemilm Wm mtmducfe lzltemal tial 4, and a current indicating device 3, strgsseslm gg glyer i gi i de- The plating operation is continued at a given poslt extreme y bn e an Wea empera ures current density depending upon the solution or It is an object of my invention to provide an both uIl'fill P ed layer 1: dfigtis i tefid p'ggser improved method. for the plating of rhenium ably havmg a thlfkness 0 which is free from the objections found in the In the electrolqlatmg Solutlon g? 13E Fknownmethoda Another important object of a current denslty of 10 to 14 atnp/dmr 1s i my invention is to provide rhenium plated articles factory- The Plated cathode-1.5 h removed from the electroplating solution.

'of practical use, such asa cathode emitter for electron discharge tubescomprising a layer of Iplated rhenium upon a, refractory base metal such'as tungsten. A further object of my invention is to provide articles of pure rhenium such :as seamless hollow cylinders, rail and ribbon.

5 Claims. (01. 204-37) i 2 Other objects and advantages of the invention will be apparent from the following description and from the accompanying drawings.

Fig. 1 illustrates schematically one form of apther sulphate plating. baths which maybe employed successfully include: pcrrhenic acid, HREO4, 20 grams per liter; concentrated sulphuric acid tobring the solution to pH=0."1 to 1.2; the temperature between 25 to 30 0.; ourrent density, to amp./dm Another sulphate bath may consist of potassium perrhenate, KReOr, 10 to 25 grams per liter; concentrated sulphuric acid to bring the solution to pH=0.80 to 1.00; the temperature between 25 to 45 0.; current density 10 to 16 amp/dm A phosphate bath maybe used, for example, potassium perrhenate, KReOi, 3 grams; phosphoric acid, sp. gr. 1.7, 7.0 cc.; sodium phosphate, NA2HPO4, 16.5 grams; water, 250 cc.; temperature between 8090 0.; pH at 90 C., 2.282; pH at 80 C., 1.743; and current density from 13 to 17 amp/dm Fig. 2 shows a further step in the process according to the invention. The cathode 2, now plated, is introduced into a reducing atmosphere 6, within a suitable enclosure 1. Such a reducing atmosphere may be composed by way of example, of hydrogen. While the cathode 2 is within the reducing atmosphere the temperature of the cathode is raised to a high temperature for a short period of time. a temperature of 1000 C. to be satisfactory for the plating of refractory metals; but the melting point of the metal to be plated must be considered. The foregoing may be easily accomplished when cathodes having a uniform cross section, by introducing a source of electric energy 8, at each end of the plated cathode introducing a sufiicient current flow in the oathode to cause it to reach the desired temperature. In the case of cathodes of other shapes, induction or furnace heating has been found desirable.

After the cathode has been fired in accordance with the foregoing, it is returned to the electroplating process for further electrodeposition as shown in Fig. 1. The entire process of electrodeposition and heat treatment, as outlined, is repeated until a layer of rhenium having the desired thickness has been obtained. The plating of rhenium in relatively thin layers as described and the subsequent firing apparently serves to alter the crystallographic structure of the plated rhenium upon the base metal. Simultaneously the objectionable internal stresses that I found when a large deposit of rhenium is plated and fired are eliminated. These stresses will cause a failure of the plated material.

The effect of the plating process may be studied by X-ray diffraction analysis. Massive rhenium, when subject to X-ray diffraction analysis. displays a spectra of lines as illustrated in Fig. 3a. With the plating of rhenium upon a given base metal, the plating displays a structure which is apparently non crystalline as indicated by the lack of lines, Fig. 3c. It is this structure that is obtained when rhenium is plated without the process as described in my invention. This plating is subject to the attack of moist air and the subsequent oxidation of the plated rhenium to perrhenic acid. However, in comparison with an X-ray diffraction photograph of tungsten, as shown in Fig. 3b, it mat be seen that even the non crystalline electrodeposition of Fig. 30 upon the base metal tungsten shows none of the characteristic lines of tungsten perceptible through the plated layer.

Upon the heat treatment of the plated cathode in accordance with the procedure heretofore described, the plated rhenium layer appears, by X-ray difiraction as shown in Fig. 3d. The non crystalline structure. of the electrodep-osition has disappeared and is replaced by the chara I have found teristic crystalline structure first seen in the X- ray diifraction photograph of massive rhenium, per se, Fig. 3a. It is to be noted that still no characteristic lines of tungsten may be found visible through the plated layer of rhenium after treatment; indicative of the fact that a massive coating of rhenium has been deposited on the base metal, and that the coating has not split to reveal the underlying tungsten base.

Such articles as seamless hollow cylinders, foil and ribbon may be made by plating a suitably shaped base metal according to the invention. A base metal for this purpose should have a melting point above 1000 C. and should be soluble in reagents that do not affect rhenium. For example such a reagent may be hydrochloric acid, HCl. Subsequent immersion of the plated article i-n hydrochloric acid will errode the base metal, leaving the desired article of pure rhenium.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. The process of plating a predetermined thickness of rhenium upon a tungsten base, comprising the steps of electrodepositing on said tungsten base a first deposited layer of rhenium having a non crystalline structure and a thickness substantially between 0.0001" to 0.0003", heating the said electrodeposited rhenium in a reducing atmosphere to a temperature of ap proximately 1000 C. and converting the said first deposited layer to rhenium having a crystalline structure, electrodepositing on' the first crystalline rhenium layer a second deposit of rhenium, heating said second deposit of rhenium and converting the said second deposit to rhenium having a crystalline structure, and repeating the said electrodeposition and heating steps until the predetermined thickness of electrodeposited crystalline rhenium is produced.

2. A method of forming on a base of refractory metal a covering of substantial thickness of pure stable rhenium in crystalline form having an X-ray diffraction pattern containing all of the characteristic lines of crystalline rhenium which comprises the steps of electro-depositing on the base a thin layer of amorphous rhenium, transforming the amorphous rhenium layer into a layer of crystalline rhenium y heating the same in a reducing atmosphere at a temperature at which the rhenium crystallizes without melting, and successively repeating the steps until a coating of crystalline rhenium of substantial thickness is obtained.

3. A method of forming on a base of tungsten a stable covering of substantial thickness of pure stable rhenium in crystalline form having an X-ray diffraction pattern containing all of the characteristic lines of crystalline rhenium which comprises the steps of elcctro-depositing on the tungsten base a thin layer of amorphous rhenium, transforming the amorphous rhenium layer into a layer of crystalline rhenium by heating the same in a reducing atmosphere at a temperature at which the rhenium crystallizes without melting, and successively repeating the steps until a coating of crystalline rhenium of substantial thickness is obtained.

4. A method of forming on a base of tungsten a stable covering of substantial thickness of pure stable rhenium in crystalline form having an X-ray diffraction pattern containing all of the characteristic lines of crystalline rhenium which comprises the steps of electro-depositing on the tungsten base a thin layer of amorphous rhenium. transforming the amorphous rhenium into a layer of crystalline rhenium layer by heating the same in a reducing atmosphere at a temperature of about 1000 C. and successively repeating the steps until a coating of crystalline rhenium of substantial thickness is obtained.

5. A method of forming on a base of refractory metal a covering of substantial thickness of pure stable rhenium in crystalline form having an X-ray diffraction pattern containing all of the characteristic lines of rhenium which comprises the steps of electrodepositing on the base a thin layer of amorphous rhenium, transforming the amorphous rhenium into a layer of crystalline rhenium by heating the same in a. reducing at mosphere at a temperature of about 1000 C and successively repeating the steps until a coating of crystalline rhenium of substantial thickness is 20 obtained.

ROBERTO LEVI.-

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,565,724 Fonda Dec. 15, 1925 1,838,273 McBride Dec. 29, 1931 2,138,573 Fink et a1 Nov. 29, 1938 2,149,656 Armstrong et al. Mar. 7, 1939 2,195,499 Schofleld Apr. 2, 1940 2,512,141 Ma et al. June 20, 1950 OTHER REFERENCES Mellor, Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 12, (1932) p. 468.

Fink et a1, Transactions Electrochemical Society, vol. 66, (1934). pp. 471-474.

Holeman, Zeitschriit 'fur anorganische und Allgemeine Chemie, vol. 202, (1931), pp. 277-291.

Young, Metal Industry, vol. 34, (1936), pp. 176-177. 

2. A METHOD OF FORMING ON A BASE OF REFRACTORY METAL A COVERING OF SUBSTANTIAL THICKNESS OF PURE STABLE RHENIUM IN CRYSTALLINE FORM HAVING AN X-RAY DIFFRACTION PATTERN CONTAINING ALL OF THE CHARACTERISTIC LINES OF CRYSTALLINE RHENIUM WHICH COMPRISES THE STEPS OF ELECTRO-DEPOSITING ON THE BASE A THIN LAYER OF AMORPHOUS RHENIUM, TRANSFORMING THE AMORPHOUS RHENIUM LAYER INTO A LAYER OF CRYSTALLINE RHENIUM BY HEATING THE SAME IN A REDUCING ATMOSPHERE AT A TEMPERATURE AT WHICH THE RHENIUM CRYSTALLIZES WITHOUT MELTING, AND SUCCESSIVELY REPEATING THE STEPS UNTIL A COATING OF CRYSTALLINE RHENIUM OF SUBSTANTIAL THICKNESS IS OBTAINED. 